Pet/mri device, pet device, and image reconstruction system

ABSTRACT

A PET/MRI device includes an MRI device that has a measurement port, a PET detector that can be inserted into the measurement port, and a mechanism that can slide the PET detector into and out of the MRI measurement port. Thereby, the PET/MRI device allows MRI measurement during PET measurement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a PET/MRI device and a PET device, andmore particularly to a PET/MRI device that can obtain a PET image and anMRI image almost simultaneously in a short time, and a PET device whosePET detector can be brought close to a measurement object for improvedsensitivity.

2. Description of the Related Art

PET/CT devices such as shown in FIGS. 1A and 1B have been in widespreaduse, in which a CT device 100 and a PET device 200 are combined toprovide a functional image of the PET device 200 superposed on amorphological image of the CT device 100 for diagnosis. In the diagrams,10 denotes a patient or subject (hereinafter, referred to generically asa patient) to be measured (tested); 20 denotes a bed on which thepatient 10 is put (lies); 22 denotes a device for moving the bed 20 in ahorizontal direction; 102 denotes an X-ray tube which is the X-raysource of the CT device 100; 104 denotes an X-ray detector; and 202denoted detector rings (hereinafter, also referred to simply as rings)which constitute the PET detector of the PET device 200. The CT exposureis typically several times the PET exposure and is therefore notnegligible.

Instead of the CT device, an MRI device which can obtain morphologicalimages without radiation exposure is receiving attention. A PET/MRIdevice capable of obtaining both PET and MRI images has been underresearch and development. In particular, there has been developed aPET/MRI device of semiconductor light receiving element type in whichall the detector units of the PET device are arranged within the staticmagnetic field of the MRI, using magnetically insensitive avalanchephotodiodes (APDs) or Geiger mode APDs (also referred to as SiPMs) asthe light receiving elements, and this PET/MRI device can be applied tothose for small animals and for the heads (See the following non-patentand patent documents: Schlyer D et al. “A Simultaneous PET/MRI scannerbased on RatCAP in small animals,” IEEE Nuclear Science SymposiumConference Record, Volume: 5, pp. 3256-3259, 2007; Schlemmer H W at al.“Simultaneous MR/PET Imaging of the Human Brain: Feasibility Study,”Radiology, 2008: 248, 1028-1035; Judenhofer M S et al. “SimultaneousPET-MRI: a new approach for functional and morphological imaging,” NetMed 2008, 14(4): 459-65; U.S. Pat. No. 7,626,392 B2; U.S. PatentApplication Laid-Open No. 2008/0287772 A1; and U.S. Patent ApplicationLaid-Open No. 2009/0108206 A1).

Given detectors of the same sensitivity, the PET device typicallyincreases in sensitivity as the detectors are located closer to thepatient and as the field of view in the direction of the body axis ofthe patient (referred to as axial field of view) is widened. The axialfield of view of the PET device as wide as the effective axial field ofview of the MRI device (30 to 40 cm or so), which is determined by thestable area of the static magnetic field, has had the problem ofinsufficient sensitivity of the PET device, requiring a PET measurementtime longer than the MRI measurement time (typically several minutes).

SUMMARY OF THE INVENTION

The present invention has been achieved in order to solve the foregoingconventional problem. It is thus a first object of the present inventionto make it possible to obtain a PET image and an MRI image almostsimultaneously in a short time.

A second object of the present invention is to improve the sensitivityof the PET detector.

The foregoing first object of the present invention has been achieved bythe provision of a PET/MRI device including: an MRI device that has ameasurement port; a PET detector that is insertable into the measurementport; and a mechanism that is capable of sliding the PET detector intoand out of the measurement port of the MRI device, MRI measurement beingallowed during PET measurement.

The PET detector may have a measurement field of view having a widthwider than that of the MRI device in a longitudinal direction of ameasurement object.

The PET detector may be movable through the measurement port with themeasurement object.

The foregoing second object has been achieved by the PET detector beingattached to a bed of the measurement object for integral movement.

The PET/MRI device may include a mechanism that is capable of slidingthe PET detector in a longitudinal direction of the bed on which themeasurement object is put.

An MRI RF coil may be attached to inside the PET detector.

The MRI RF coil attached to inside the PET detector may be a transmittercoil, a receiver coil, a transmitter-receiver two-way coil, or a coilthat includes both a transmitter coil and a receiver coil.

The width of the measurement field of view of the PET detector may beextended to cover the measurement object at least from its head to itstrunk.

The PET detector may be divided in the longitudinal direction of themeasurement object.

Detector rings that constitute the PET detector, and/or detector unitsthat constitute the detector rings, may be arranged at nonuniformintervals.

PET detectors having different resolutions and/or sensitivities may beused for the head and the trunk, respectively.

The PET detector for a head may have a resolution higher than that ofthe PET detector for a trunk.

The PET detector for the head may include a detector ring that has aninner diameter smaller than that of a detector ring that constitutes thePET detector for the trunk.

The PET detector may have an opening in at least an eye-covering areanear the head of the measurement object.

A detector ring that constitutes the PET detector near a trunk of themeasurement object may have a sectional shape such that its size in athickness direction of the measurement object is different from that ina width direction perpendicular to the thickness direction so that thedetector approaches a surface of the trunk.

The detector ring that constitutes the PET detector near the trunk ofthe measurement object may include an arched upper half portion and anarched lower half portion in the thickness direction of the measurementobject, the arched upper half portion having a radius of curvaturesmaller than that of the arched lower half portion.

The detector ring that constitutes the PET detector may have a detectorring that has an arched upper half portion in the thickness direction ofthe measurement object, the arched upper half portion being openable atleast in part.

The arched upper half portion may be opened in a double-doorconfiguration.

The arched upper half portion may be opened in a single-doorconfiguration.

The arched upper half portion and a remaining arched lower half portionmay be separable from each other.

The detector ring that constitutes the PET detector may have an archedupper half portion in the thickness direction of the measurement object,the arched upper half portion being variable in size and/or in shapeaccording to the measurement object.

The PET detector for a head may be movable with respect to and/ordetachable from the PET detector for a trunk.

The PET measurement may be started before the PET detector starts beingslid into the MRI measurement port, and ended after the PET detectorends being slid to a retracted position of the measurement object afterend of the MRI measurement, whereby PET measurement time is maximized.

The PET detector may include a mechanism for sliding inside themeasurement port independent of a sliding movement of the measurementobject, so that the PET detector can slide at a moving speed lower thanthat at which the measurement object slides.

The PET/MRI device may include a slide mechanism that is capable ofretracting the PET detector into the MRI measurement port so as tofacilitate loading and unloading of the measurement object onto/from thebed and setup of the measurement object.

The PET measurement may be started immediately before start of the MRImeasurement and ended immediately after end of the MRI measurement, orPET data that is collected from immediately before the start of the MRImeasurement to immediately after the end of the MRI measurement may beused for PET image reconstruction processing, so as to improvesimultaneity between the PET measurement and the MRI measurement.

The second object of the present invention has also been achieved by theattachment of a PET detector to a bed of a measurement object.

The present invention also provides a PET device including a belt-likePET detector that is composed of detector units connected by links, thedetector units being freely changeable in layout according to a shape ofa measurement object.

The links may have a function of allowing rotation and a change indistance between the detector units.

The links may include an encoder so that a relationship in spatialposition coordinates between adjoining detector units is obtainable.

The PET device may include an inner frame so that the detector unitsconstituting the belt-like PET detector are located in predeterminedpositions.

A plurality of types of the inner frame may be prepared in advanceaccording to size and/or shape of the measurement object.

The present invention also provides an image reconstruction system whichcalculates a system matrix element for use in an image reconstructionoperation by: referring to a relationship in spatial positioncoordinates between adjoining ones of detector units that are connectedinto a belt-like PET detector by links, the relationship being acquiredfrom encoders attached to the links; referring to spatial positioncoordinates of the detector units constituting the belt-like PETdetector, the coordinates being determined by an inner frame forlocating the detector units in predetermined positions; or referring tospatial position coordinates of the detector units, determined by anarched upper half portion of the PET detector.

System matrices corresponding to respective layout patterns of thedetector units may be calculated in advance and stored in a storingdevice, the layout patterns being uniquely determined by types of theinner frame or the arched upper half portion of the PET detector.

According to the present invention, it is possible to bring the PETdetector close to the patient and/or make the effective measurementfield of view of the PET detector wider than that of the MRI device, sothat a PET image and an MRI image are obtained almost simultaneously ina short time.

The PET detector can be attached to the bed of the measurement object sothat the PET detector comes closer to the measurement object for evenhigher sensitivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view and FIG. 1B is a sectional view seen fromthe front, showing the configuration of an example of a conventionalPET/CT device;

FIG. 2 is a perspective view showing a general configuration of a firstembodiment of the present invention;

FIG. 3A is a front view and FIG. 3B is a sectional view seen from aside, showing a detailed configuration of the same;

FIGS. 4A and 4B are sectional views showing a typical operation of thesame;

FIGS. 5A and 5B are flowcharts showing operating procedures of the same;

FIG. 6 is a time chart of the same;

FIG. 7 is a time chart of a modification of the same;

FIG. 8 is a time chart of another modification of the same;

FIG. 9A is a perspective view showing a general configuration of asecond embodiment of the present invention, and FIG. 9B is a sectionalview seen from a side, showing a detailed configuration of the same;

FIGS. 10A and 10B are cross-sectional views of the same, showing a statewhere an RF coil is attached;

FIG. 11A is a front view and FIG. 11B is a sectional view seen from aside, showing a detailed configuration of a third embodiment of thepresent invention;

FIG. 12A is a sectional view seen from a side, showing the configurationof essential parts of a fourth embodiment, and FIG. 12B a fifthembodiment, of the present invention;

FIG. 13 is a perspective view showing a general configuration of a sixthembodiment of the present invention;

FIG. 14 is a sectional view of the same seen from a side;

FIG. 15 is a perspective view showing a general configuration of aseventh embodiment of the present invention;

FIGS. 16A to 16C are longitudinal sectional views showing theconfiguration of essential parts of the seventh embodiment;

FIGS. 17A, 17B, and 17C are cross-sectional views showing the layout ofthe PET detectors for slender type, stout type, and the head,respectively;

FIGS. 18A and 18B are cross-sectional views showing the configurationand operation of an eighth embodiment of the present invention;

FIG. 19 is a perspective view of the same;

FIGS. 20A and 20B are cross-sectional views showing the configurationand operation of a modification of the eighth embodiment;

FIGS. 21A and 21B are perspective views showing the configuration andoperation of essential parts of a ninth embodiment of the presentinvention;

FIG. 22 is a perspective view showing the configuration of essentialparts of a tenth embodiment of the present invention;

FIG. 23 is a perspective view showing the configuration of essentialparts of a belt-like PET detector used in the tenth embodiment;

FIG. 24 is a block diagram showing signal processing and imagereconstruction processing according to the tenth embodiment;

FIGS. 25A and 25B are cross-sectional views showing examples of thelayout of the belt-like PET detector;

FIGS. 26A and 26B are perspective views showing the configuration andoperation of essential parts of an eleventh embodiment of the presentinvention;

FIG. 27 is a perspective view showing the configuration of joints of thebelt-like PET detector used in the eleventh embodiment;

FIG. 28 is a perspective view showing the state where the belt-like PETdetector of the eleventh embodiment is being attached to an inner frame;

FIGS. 29A and 29B are cross-sectional views showing examples of theattached state;

FIG. 30 is a perspective view showing a belt-like PET detector used in atwelfth embodiment of the present invention;

FIG. 31 is a perspective view showing the configuration of joints of thesame;

FIGS. 32A and 32B are cross-sectional views showing examples of theattached state;

FIG. 33 is a perspective view showing an inner frame that is used in amodification of the twelfth embodiment;

FIG. 34 is a perspective view showing the configuration of a thirteenthembodiment of the present invention;

FIGS. 35A and 35B are perspective views showing the configuration ofessential parts of a fourteenth embodiment of the present invention;

FIG. 36A is a cross-sectional view and FIG. 36B is a plan view of thesame;

FIG. 37A is a front view and FIG. 37B is a sectional view seen from aside, showing the overall configuration of a fifteenth embodiment of thepresent invention;

FIGS. 38A to 38C are sectional views showing the operating state of thefifteenth embodiment;

FIG. 39A is a front view and FIG. 39B is a sectional view seen from aside, showing the overall configuration of a sixteenth embodiment of thepresent invention;

FIGS. 40A to 40C are sectional views showing the operating state of thesame;

FIGS. 41A to 41C are sectional views seen from a side, showing theoperating state of a seventeenth embodiment of the present invention;

FIG. 42A is a front view and FIG. 42B is a sectional view seen from aside, showing the overall configuration of an eighteenth embodiment ofthe present invention;

FIG. 43 is a perspective view showing the configuration of essentialparts of a nineteenth embodiment of the present invention;

FIG. 44 is a perspective view showing the configuration of essentialparts of a twentieth embodiment of the present invention;

FIG. 45 is a sectional view seen from a side, showing the overallconfiguration of the same; and

FIGS. 46A to 46C are sectional views showing the operating state of thesame.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings.

As shown in FIG. 2 (a perspective view for overview), FIG. 3A (a frontview), and FIG. 3B (a sectional view seen from a side), a firstembodiment of the present invention includes an MRI device 300 and a PETdetector 210. The MRI device 300 has a measurement port (here, a patientport) 302. The PET detector 210 has an outer diameter smaller than theinner diameter of the patient port 302, and can move through the patientport 302 with a measurement object (here, a patient) 10. The PETdetector 210 has an effective measurement field of view (referred to asa PET field of view) P wider than the effective measurement field ofview (referred to as MRI field of view) M of the MRI device 300, therebyallowing MRI measurement during PET measurement. In the diagrams, 24denotes a cushion for protecting the patient 10, and 304 denotes an RFcoil for the MRI device 300. The RF coil 304 may be integrated with thecushion 24 at the back side of the patient.

The MRI field of view M is determined by the area where the staticmagnetic field is stable, which is typically 30 to 40 cm or so. The PETfield of view P can be extended to improve the sensitivity of the PETmeasurement. A PET image of sufficient image quality can thus beobtained in a PET measurement time comparable to the MRI measurementtime.

The PET detector 210 is capable of stable operation in the MRI magneticfield environment. Examples include APD-bottomed scintillator blocks,and a Depth-of-Interaction (DOI) detectors having a three-dimensionalarray of semiconductor light receiving elements on the surface of athree-dimensional array of small scintillator elements, which has beenproposed by the inventors in Japanese Patent Application Laid-Open No.2009-121929 and in Y. Yazaki, H. Murayama, N. Inadama, A. Ohmura, H.Osada, F. Nishikido, K. Shibuya, T. Yamaya, E. Yoshida, T. Moriya, T.Yamashita, and H. Kawai, “Preliminary study on a new DOI PET detectorwith limited number of photo-detectors,” The 5th Korea-Japan JointMeeting on Medical Physics, Sep. 10-12, 2008, Jeju, Korea, YI-R2-3,2008. DOI detectors can be used to suppress a drop in resolution even inclose proximity. The closer access can also reduce resolutiondegradation due to angular deviations, as well as increase the solidangle to improve the sensitivity even with a relatively small number ofdetectors.

In the present embodiment, the PET detector 210 is integrated with a bed20. That is, part of the PET detector 210 also functions as a bed. Sincethe PET detector can be brought closest to the patient, the solid angleincreases for improved sensitivity and fast measurement.

The RE coil 304 is installed so as to cover the PET field of view P andmost of the axial field of view. The RE coil 304 is arranged inside(within the inner diameter of) the PET detector 210 since the closer theRF coil 304 is to the patient 10, the higher the signal S/N ratiobecomes. Another reason is to prevent electrical noise and the like fromthe PET detector 210. The RF coil is highly transparent to annihilationradiations. The presence of the RF coil 304 thus has only a limitedimpact on the PET measurement.

The bed 20 may be moved by a bed moving device 22 at constant speed orstep by step.

FIG. 4A shows the state at the start of the MRI measurement. FIG. 4Bshows the state at the end of the MRI measurement. In FIGS. 4A and 4B,the moving speed Vb of the bed, if constant, is given by Vb=(P−M)/Tm. Tmis the MRI measurement time.

FIG. 5A shows a procedure in which the PET measurement time Tp ismaximized to increase the data collection time for improved PET imagequality. FIG. 5B shows a procedure in which the PET measurement isstarted immediately before the start of the MRI measurement and endedimmediately after the end of the MRI measurement, or PET data that iscollected from immediately before the start of the MRI measurement toimmediately after the end of the MRI measurement is used for PET imagereconstruction processing. Such a procedure makes the PET measurementtime and the MRI measurement time almost equal, thereby ensuringsimultaneity between the PET measurement and the MRI measurement. For abreath-held shot, the procedure of FIG. 5B is preferred.

FIG. 6 shows the time chart. For the bed position, the positions of thefront and rear ends of the bed are plotted. Suppose that the PETmedicine has been administered to the patient in advance. In FDG-PET, itis typically administered an hour earlier.

In FIG. 6, the maximum value Tpmax of the PET measurement time shows adifference in time between when the PET detector 210 is attached inplace and when the PET detector 210 is detached or moved.

The actual Tp is determined by the following formula:

Tm≦Tp≦Tpmax.  (1)

According to the procedure of FIG. 5A, Tp approaches Tpmax. With theprocedure of FIG. 5B, Tp approaches Tm.

The MRI measurement start position and the MRI measurement end portionneed not necessarily be set at the respective ends of the MRI field ofview M. For example, as in a modification shown in FIG. 7, the MRImeasurement start position and the MRI measurement end position both maybe at the center of the MRI field of view where a favorable magneticfield is formed.

During the MRI measurement, the bed may be slid step by step, not atconstant speed.

In FIGS. 6 and 7, the MRI measurement is performed while the bed ismoving on one way. However, as in another modification shown in FIG. 8,the MRI measurement may be performed on both ways of the reciprocatingmovement. In such a case, MRI measurement 1 onward and MRI measurement 2on the return may be performed by the same sequence. Different sequencesmay be combined, for example, so that MRI measurement 1 is T1-weightedand MRI measurement 2 is T2-weighted.

The foregoing first embodiment has dealt with the case where the PETdetector 210 has a uniform configuration in the longitudinal directionof the measurement object, or the direction of the body axis of thepatient 10 here. As in a second embodiment shown in FIG. 9A, the PETdetector 210 may be divided into a head PET detector 212 and a trunk orbody PET detector 214. FIG. 9B shows a sectional view of a concreteexample of the second embodiment seen from a side. FIGS. 10A and 10Bshow cross-sectional views of the body and head portions of the PETdetector. The body PET detector has an elliptical cross section, whereasit may be circular.

In the present embodiment, the head PET detector 212 and the body PETdetector 214 are fixed to the bed 20 so that they can be horizontallymoved with the patient 10 by the bed moving device 22.

Coincidence measurement between the head PET detector 212 and the bodyPET detector 214 can prevent a drop in the accuracy of the reconstructedimage near the border between the head PET detector 212 and the body PETdetector 214.

The head PET detector 212 and the body PET detector 214 may be spacedapart by using the technology of the open PET device that the inventorshave proposed in WO 2009/133628 A1. In the absence of the space as inFIGS. 9A and 9B, the PET field of view P equals to the head field ofview H+the body field of view B.

The RE coil may be a transmitter-receiver two-way coil, a transmittercoil, or a receiver coil. The RF coil and the PET detector may be formedas separate members. When the RF coil and the PET detector areintegrated as shown in FIGS. 10A and 10B, the following combinations arepossible:

A transmitter-receiver two-way RE coil is integrated into inside the PETdetector.

Only a transmitter RE coil is integrated into inside the PET detector,and a receiver RF coil is separately arranged so as to cover thepatient.

A transmitter RF coil is built in the main unit of the MRI device, andonly a receiver RE coil is integrated into inside the PET detector.

In FIGS. 10A and 10B, 218 denotes a cover, 312 denotes a head RE coil,and 314 denotes a body RE coil.

FIG. 11A is a front view showing a concrete example of a thirdembodiment which is a modification of the second embodiment. FIG. 11B isa sectional view seen from a side.

In the present embodiment, the head PET detector 212 is fixed to the bed20. The body PET detector 214 can be horizontally moved by a PETdetector moving device 220, independent of the bed 20. In the diagrams,320 designates rollers that support the PET detector 214 in the patientport 302.

The head PET detector 212 and the body PET detector 214 have differentcenter positions in the patient port 302 of the MRI device 300. The bedmoving device 22 may include a bed up-down mechanism 26 so that the headPET detector 212 and the head RF coil 312 can be slid and moved up anddown with the patient 10. The body PET detector 214 and the body RE coil314 are only moved to slide horizontally, without up and down movements.

The PET detector may be made of a combination of detectors of differentresolutions depending on the locations. FIG. 12A shows a fourthembodiment in which high-resolution detectors are arranged in thevicinity of the head where high resolution is needed. FIG. 12B shows afifth embodiment with a reduced number of detectors, in which thedetectors are spaced wider, instead of the sensitivity being lowered,for the lower body or the legs in particular where not so highsensitivity is needed.

As in a sixth embodiment shown in FIG. 13 (a perspective view) and FIG.14 (a sectional view seen from a side), the technology of the open PETdevice may be used to form an open area in the head PET device 212 inthe vicinity of the field of view so as to alleviate the sense ofconfinement on the head.

As in a seventh embodiment shown in FIG. 15, the body PET detector 214may be made of noncircular (in the diagram, elliptical) rings so thatthe PET detector comes closer to the patient's body.

FIGS. 16A to 16C show the configuration of essential parts where thedetector rings can be changed in size according to the body type of thepatient 10. FIG. 16A shows an example where normal-sized detector rings214 a are used.

FIG. 16B shows an example where large-diametered detector rings 214 bare used for the abdomen. FIG. 16C shows an example where thelarge-diametered detector rings 214 b are used not only for the abdomenbut for the entire body.

FIGS. 17A to 17C show the cross sections of FIGS. 16A to 16C. FIG. 17Ashows a PET detector layout for slender type, FIG. 17B shows a PETdetector layout for stout type, and FIG. 17C shows a PET detector layoutfor the head. In the PET detector layout for stout type of FIG. 17B, thearched half portion of the detector on the bed side (lower side in thethickness direction) and that on the opposite side (upper side in thethickness direction) are arranged along the curves of respectivedifferent curvatures.

The cells in the diagrams represent scintillator blocks or detectorunits.

In an eighth embodiment shown in FIGS. 18A and 18B, an arched half PETdetector 224 on the upper side in the thickness direction is openable,for example, in a double-door configuration so as to facilitate settingup the patient 10. In the diagrams, 222 denotes the lower (bed-side) PETdetector, and 226 denotes hinges.

Since the PET detector is heavy in weight, it may be divided intoseveral sections as shown in FIG. 19 (six sections in FIG. 19).

As in a modification shown in FIGS. 20A and 20B, the PET detector may beformed in a single-door configuration.

Alternatively, as in a ninth embodiment shown in FIG. 21, the PETdetector may be configured so that it is divided into an arched halfdetector 222 on the bed side (lower side in the thickness direction) andan arched half detector 224 on the opposite side (upper side in thethickness direction). Various sizes of upper detectors 224 may beprovided according to the body type.

As in a tenth embodiment shown in FIG. 22, detector units 204 may beconnected into a belt-like configuration by links 232. The samebelt-like PET detectors 230 can be used to form various sizes ofdetector rings according to the body type. In the lower half, or the bedportion, the detector units 204 are fixed by fixing wires 234, forexample.

As shown in FIG. 23, encoders 236 for acquiring angular information areattached to the joints of the detector units 204 on the upper side inthe thickness direction. As shown in FIG. 24, relative positions betweenthe detector units 204 (the relationship in spatial position coordinatesbetween adjoining detector units) can thus be acquired to obtain atomographic image by image reconstruction calculations.

With reference to FIG. 24, a description will be given of therelationship between the encoders 236 and an image reconstructionworkstation (WS) 400 when the layout pattern of the PET detector ischanged according to the subject's body type. Pairs of annihilationradiations detected by the PET detector 204 are processed intomeasurement data by a data collection system 500 through coincidenceprocessing, data collection processing, etc. The measurement data istransmitted to the image reconstruction WS 400 for image reconstructionprocessing before output as a tomographic image. The imagereconstruction needs accurate detector positions, or it is not possibleto calculate the system matrix. The encoders 236 are then used to graspthe relationship in spatial position coordinates between the adjoiningdetector units, thereby grasping the positions of the respectivedetectors.

Specifically, the encoders 236 provide relative angular information onthe joints between the detectors. The information is transmitted to theimage reconstruction WS 400. The detector coordinates are initiallydetermined by detector coordinate calculation processing. The systemmatrix is then calculated based on the detector coordinates. For theimage reconstruction processing, a whole system matrix calculated may beread at a time. Or, necessary system matrix elements may be calculatedby on-the-fly processing when needed.

FIG. 25A shows a case with small detector rings according to the tenthembodiment. FIG. 25B shows a case with large detector rings.

As in an eleventh embodiment shown in FIGS. 26A and 26B, large and smallinner frames 30 attachable to the bed 20 may be prepared for respectivebody types. This makes it possible to accurately and easily grasp thespatial position coordinates (detector positions) of the belt-like PETdetector 230 having no encoders such as shown in FIG. 27. Such innerframes 30 are formed to have high rigidity as well as high transparencyto radiation. For example, the inner frames 30 are made of reinforcedplastic.

FIG. 28 shows the state where the belt-like PET detector 230 is beingattached to an inner frame 30 according to the eleventh embodiment.FIGS. 29A and 29B show attached states. FIG. 29A shows an example ofsmall ring size, and FIG. 29B shows an example of large ring size.

The belt-like PET detector 230 may not only allow free rotations of thedetector units 204, but also make the distances between the detectorunits 204 variable as in a twelfth embodiment shown in FIG. 30. FIG. 31shows the joints in detail.

FIG. 32A shows the state of attachment of small ring size according tothe twelfth embodiment. FIG. 32B shows the state of attachment of largering size. Rings of different sizes can be formed by using the samenumber of detectors (in FIGS. 32A and 32B, eight movable detector units)without redundant detectors as in FIG. 29A.

As in a modification of the twelfth embodiment shown in FIG. 33,positioning recesses 30 a may be formed in the inner frame 30 so as tofix the detector positions.

Now, a description will be given of the image reconstruction processingwhen various sizes of arched upper half detectors 224 and inner frames30 are prepared in advance and appropriate ones are selected accordingto the patient's body type (size and shape) as in the ninth embodimentshown in FIGS. 21A and 21B or the eleventh embodiment shown in FIGS. 26Aand 26B. Since the layout of the detector units is uniquely determinedby the size and shape of the upper detector 224 or inner frame 30selected, it is possible to acquire the spatial position coordinates ofthe detector units without encoders. Specifically, the type of the upperdetector 224 or inner frame 30 selected may be entered by the user froma console. Identification tags may be attached to the upper detectors224 or inner frames 30 so that the type used is automatically detectedon the side of the bed 20.

As shown in FIG. 24, the system matrix may be calculated each time basedon the detector coordinates. Since the types of the upper detectors 224or inner frames 30 for use are limited, system matrices corresponding tothe respective patterns of detector layout may be calculated in advanceand stored into a storing device in the image reconstruction WS as adata set.

The belt-like PET detectors may be used not only for the head and body,but also for some specific areas. FIG. 34 shows a thirteenth embodimentwhich shows another application example of the belt-like PET detectors.Here, a belt-like PET detector 230 for arms is wound around the arm. Thereference numeral 40 denotes a table on which the belt-like PET detectoris placed.

For example, dynamic function measurement on the head, using a head PETdevice (not shown in the diagram), is not easy to perform since arterialblood needs to be sampled at time intervals of several seconds toseveral minutes. The combined use of the head PET device and thebelt-like PET detector wound around the arm can facilitate the dynamicfunction measurement since it is possible without arterial bloodsampling to measure the concentration and flow rate of RI flowingthrough the arteries in the arm. Aside from arterial blood sampling, thebelt-like PET detector also allows area-specific high-precisiondiagnostic imaging. Examples of the area include the arms as well as thefeet, joints, neck, and breast.

In a fourteenth embodiment shown in FIGS. 35A and 35B, the head PETdetector 212 can be slid over guide rails 21 of the bed 20 in thedirection of the body axis so as to facilitate setting up the patient10. FIG. 36 shows the slide mechanism in detail. The head PET detector212 may be detachable.

As in a fifteenth embodiment shown in FIGS. 37A and 37B, the bed 20 andthe PET detector 210 may be independently slidable when the PET field ofview P lies between the field of view F of the RF coil and the MRI fieldof view M.

According to the present embodiment, the bed 20 and the PET detector 210can be slid at different speeds so that a wider field of viewcorresponding to the width of the field of view F of the RF coil can bemeasured by PET and MRI.

FIGS. 38A to 38C show the states from the start to the end of theexamination according to the present embodiment. Assuming that the bedmoving speed Vb and the PET detector moving speed Vp both are constant,Vp and Vb are given by the following equations:

Vp=(P−M)/T, and  (2)

Vb=(F−M)/T,  (3)

where T=the MRI measurement time=the PET measurement time.

The fifteenth embodiment has dealt with the case where the PET detectoris integrated in the direction of the body axis. As in a sixteenthembodiment shown in FIGS. 39A and 39B, the head PET detector 212 and thebody PET detector 214 may be separated from each other. The head PETdetector 212 and the bed 20 are integrated with each other, and slide ata speed of Vb. The body PET detector 214 slides at a speed of Vp.

FIGS. 40A to 40C show the states of movement from the start to the endof the examination according to the sixteenth embodiment. Assuming thatthe bed moving speed Vb and the PET detector moving speed Vp both areconstant, Vp and Vb are expressed by the following equations:

Vp=(B+H−M)/T, and  (4)

Vb=(F−M)/T,  (5)

where T=the MRI measurement=the PET measurement time.

As in a seventeenth embodiment shown in FIGS. 41A to 41C, the PETdetector (or at least the body PET detector 214) may have a mechanismfor making a movement independent of the movement of the bed 20. In sucha case, the PET detector 214 can be moved into the MRI detector 300 foreasy patient setup without a contrivance to open the PET detector.

More specifically, for patient setup, as shown in FIG. 41A, the PETdetector 214 is moved into the MRI patient port 302 so that the patient10 can easily get on the bed 20. The head PET detector 212, if used, ismoved to the left in the diagram.

Next, the RF coils 312 and 314 and the head PET detector 212 areattached as shown in FIG. 41B. Specifically, the head and body RF coils312 and 314 are initially attached. The head PET detector 212, if used,is slid for attachment. The head RE coil 312 may be integrated with thehead PET detector 212.

Finally, as shown in FIG. 41C, the bed 20 and the PET detector 214 areslid to a predetermined MRI measurement start position.

After the examination, the patient can be evacuated in order reverse tothe foregoing.

While the diagrams show the configuration where the patient enters theMRI patient port 302 head first, the MRI patient port 302 may be enteredfeet first.

As in an eighteenth embodiment shown in FIGS. 42A and 42B, a transmitterRE coil 304S may be integrally arranged inside the PET detector 210. Areceiver RE coil is arranged closer to the patient. A head RF coil 312Rand a body RF coil 314R of different sizes may be used.

FIG. 43 shows a nineteenth embodiment for measuring a local area, notthe whole body, by PET and MRI at the same time. The PET detector 210 isslidable along the guide rails 21 on the bed 20, so that the PETdetector 210 can be freely moved to the position of the area to measure.The PET detector 210 can be accurately and safely mounted on themeasurement area when outside of the MRI patient port 302. Since the PETdetector 210 mounted is slid with the patient on the bed 20, there is nodanger of displacement. The difference in level between the bed 20 andthe PET detector 210 is eliminated by the provision of cushions 24. Thecushions 24 need to be adjusted in length depending on the position ofthe PET detector 210.

FIG. 44 is a perspective view showing the configuration of essentialparts of a twentieth embodiment which is a modification of thenineteenth embodiment. The bed 20 is composed of a base 20B whichincludes the guide rails 21, and supports 20S and a cover 20C. The PETdetector 210 is arranged so that part of the ring is interposed betweenthe base 20B and the cover 20C. Such a configuration eliminates adifference in level on the cover 20C which makes contact with thepatient. In addition, the PET detector 210 can conveniently be slid toan appropriate position where to cover the measurement point with thepatient put on the bed.

FIG. 45 is a sectional view seen from a side, showing the overallconfiguration of the twentieth embodiment. Here, the RF coil 304 isintegrally arranged inside the PET detector 210.

FIGS. 46A to 46C show the operating state of the twentieth embodiment.When setting a patient on the bed, as in FIG. 46A, the bed is locatedaway from the MRI patient port 302 and the PET detector 210 is moved tothe bed end. After the patient is laid on, as in FIG. 46B, the PETdetector 210 is slid so that the measurement point (in the diagram,chest) is covered by the PET detector 210. After the completion of thepatient setup, the PET detector 210 is inserted into the MRI patientport 302 and the MRI measurement is started.

According to the present invention, it is possible to perform PET andMRI concurrent examinations and a whole-body PET/MRI examination withextremely high utility.

1. A PET/MRI device comprising: an MRI device that has a measurementport; a PET detector that is insertable into the measurement port; and amechanism that is capable of sliding the PET detector into and out ofthe measurement port of the MRI device, MRI measurement being allowedduring PET measurement.
 2. The PET/MRI device according to claim 1,wherein the PET detector has a measurement field of view having a widthwider than that of the MRI device in a longitudinal direction of ameasurement object.
 3. The PET/MRI device according to claim 1, whereinthe PET detector is movable through the measurement port with themeasurement object.
 4. The PET/MRI device according to claim 1, whereinthe PET detector is attached to a bed of the measurement object forintegral movement.
 5. The PET/MRI device according to claim 4, furthercomprising a mechanism that is capable of sliding the PET detector in alongitudinal direction of the bed on which the measurement object isput.
 6. The PET/MRI device according to claim 1, wherein an MRI RF coilis attached to inside the PET detector.
 7. The PET/MRI device accordingto claim 6, wherein the MRI RF coil attached to inside the PET detectoris a transmitter coil, a receiver coil, a transmitter-receiver two-waycoil, or a coil that includes both a transmitter coil and a receivercoil.
 8. The PET/MRI device according to claim 2, wherein the width ofthe measurement field of view of the PET detector is extended to coverthe measurement object at least from a head to a trunk thereof.
 9. ThePET/MRI device according to claim 8, wherein the PET detector is dividedin the longitudinal direction of the measurement object.
 10. The PET/MRIdevice according to claim 8, wherein detector rings that constitute thePET detector, and/or detector units that constitute the detector rings,are arranged at nonuniform intervals.
 11. The PET/MRI device accordingto claim 8, wherein PET detectors having different resolutions and/orsensitivities are used for a head and a trunk, respectively.
 12. ThePET/MRI device according to claim 11, wherein the PET detector for ahead has a resolution higher than that of the PET detector for thetrunk.
 13. The PET/MRI device according to claim 8, wherein the PETdetector for a head includes a detector ring that has an inner diametersmaller than that of a detector ring that constitutes the PET detectorfor a trunk.
 14. The PET/MRI device according to claim 1, wherein thePET detector has an opening in at least an eye-covering area near a headof the measurement object.
 15. The PET/MRI device according to claim 1,wherein a detector ring that constitutes the PET detector near a trunkof the measurement object has a sectional shape such that a size thereofin a thickness direction of the measurement object is different fromthat in a width direction perpendicular to the thickness direction sothat the detector approaches a surface of the trunk.
 16. The PET/MRIdevice according to claim 15, wherein the detector ring that constitutesthe PET detector near the trunk of the measurement object includes anarched upper half portion and an arched lower half portion in thethickness direction of the measurement object, the arched upper halfportion having a radius of curvature smaller than that of the archedlower half portion.
 17. The PET/MRI device according to claim 1, whereinthe detector ring that constitutes the PET detector has an arched upperhalf portion in the thickness direction of the measurement object, thearched upper half portion being openable at least in part.
 18. ThePET/MRI device according to claim 17, wherein the arched upper halfportion is opened in a double-door configuration.
 19. The PET/MRI deviceaccording to claim 17, wherein the arched upper half portion is openedin a single-door configuration.
 20. The PET/MRI device according toclaim 17, wherein the arched upper half portion and a remaining archedlower half portion are separable from each other.
 21. The PET/MRI deviceaccording to claim 3, wherein the detector ring that constitutes the PETdetector has an arched upper half portion in the thickness direction ofthe measurement object, the arched upper half portion being variable insize and/or in shape according to the measurement object.
 22. ThePET/MRI device according to claim 9, wherein the PET detector for a headis movable with respect to and/or detachable from the PET detector for atrunk.
 23. The PET/MRI device according to claim 1, wherein the PETmeasurement is started before the PET detector starts being slid intothe measurement port of the MRI device, and ended after the PET detectorends being slid to a retracted position of the measurement object afterend of the MRI measurement, whereby PET measurement time is maximized.24. The PET/MRI device according to claim 1, wherein the PET detectorincludes a mechanism for sliding inside the measurement port independentof a sliding movement of the measurement object, so that the PETdetector slides at a moving speed lower than that at which themeasurement object slides.
 25. The PET/MRI device according to claim 24,comprising a slide mechanism that is capable of retracting the PETdetector into the measurement port of the MRI device so as to facilitateloading and unloading of the measurement object onto/from the bed andsetup of the measurement object.
 26. The PET/MRI device according toclaim 1, wherein the PET measurement is started immediately before startof the MRI measurement and ended immediately after end of the MRImeasurement, or PET data that is collected from immediately before thestart of the MRI measurement to immediately after the end of the MRImeasurement is used for PET image reconstruction processing, so as toimprove simultaneity between the PET measurement and the MRImeasurement.
 27. A PET device comprising a PET detector attached to abed of a measurement object.
 28. The PET device according to claim 27,comprising a mechanism that is capable of sliding the PET detector in alongitudinal direction of the bed on which the measurement object isput.
 29. The PET device according to claim 27, wherein a width of ameasurement field of view of the PET detector is extended to cover themeasurement object at least from a head to a trunk thereof.
 30. The PETdevice according to claim 29, wherein the PET detector is divided in thelongitudinal direction of the measurement object.
 31. The PET deviceaccording to claim 29, wherein detector rings that constitute the PETdetector, and/or detector units that constitute the detector rings, arearranged at nonuniform intervals.
 32. The PET device according to claim29, wherein PET detectors having different resolutions and/orsensitivities are used for a head and a trunk, respectively.
 33. The PETdevice according to claim 32, wherein the PET detector for a head has aresolution higher than that of the PET detector for the trunk.
 34. ThePET device according to claim 29, wherein the PET detector for a headincludes a detector ring that has an inner diameter smaller than that ofa detector ring that constitutes the PET detector for a trunk.
 35. ThePET device according to claim 29, wherein the PET detector has anopening in at least an eye-covering area near a head of the measurementobject.
 36. The PET device according to claim 27, wherein a detectorring that constitutes the PET detector near a trunk of the measurementobject has a sectional shape such that a size thereof in a thicknessdirection of the measurement object is different from that in a widthdirection perpendicular to the thickness direction so that the detectorapproaches a surface of the trunk.
 37. The PET device according to claim36, wherein the detector ring that constitutes the PET detector near thetrunk of the measurement object includes an arched upper half portionand an arched lower half portion in the thickness direction of themeasurement object, the arched upper half portion having a radius ofcurvature smaller than that of the arched lower half portion.
 38. ThePET device according to claim 27, wherein the detector ring thatconstitutes the PET detector has an arched upper half portion in thethickness direction of the measurement object, the arched upper halfportion being openable at least in part.
 39. The PET device according toclaim 38, wherein the arched upper half portion is opened in adouble-door configuration.
 40. The PET device according to claim 38,wherein the arched upper half portion is opened in a single-doorconfiguration.
 41. The PET device according to claim 38, wherein thearched upper half portion and a remaining arched lower half portion areseparable from each other.
 42. The PET device according to claim 27,wherein the PET detector includes a detector ring at least whose upperportion above a bed covering the measurement object is variable in sizeand/or in shape according to the measurement object.
 43. The PET deviceaccording to claim 30, wherein the PET detector for a head is movablewith respect to and/or detachable from the PET detector for a trunk. 44.A PET device comprising a belt-like PET detector that is composed ofdetector units connected by links, the detector units being freelychangeable in layout according to a shape of a measurement object. 45.The PET device according to claim 44, wherein the links has a functionof allowing rotation and a change in distance between the detectorunits.
 46. The PET device according to claim 44, wherein the linksincludes an encoder so that a relationship in spatial positioncoordinates between adjoining detector units is obtainable.
 47. The PETdevice according to claim 44, comprising an inner frame so that thedetector units constituting the belt-like PET detector are located inpredetermined positions.
 48. The PET device according to claim 47,wherein a plurality of types of the inner frame are prepared in advanceaccording to size and/or shape of the measurement object.
 49. An imagereconstruction system for calculating a system matrix element for use inan image reconstruction operation by: referring to a relationship inspatial position coordinates between adjoining ones of detector unitsthat are connected into a belt-like PET detector by links, therelationship being acquired from encoders attached to the links;referring to spatial position coordinates of the detector unitsconstituting the belt-like PET detector, the coordinates beingdetermined by an inner frame for locating the detector units inpredetermined positions; or referring to spatial position coordinates ofthe detector units, determined by an arched upper half portion of thePET detector.
 50. The image reconstruction system according to claim 49,wherein system matrices corresponding to respective layout patterns ofdetector units are calculated in advance and stored in a storing device,the layout patterns being uniquely determined by types of an inner frameor an arched upper half portion of a PET detector.